fix: restore dashboard app shell

[JustAGhosT]

Summary

• render the shared header/navigation in authenticated dashboard routes
• restore readable dashboard metrics/table colors in dark mode by using design tokens
• add the missing dashboard card wrapper styles used by the page
• fix stale 404 helper links that pointed at /dashboard/dashboard and /dashboard/* route-group paths

Validation

• pnpm exec eslint 'app/(dashboard)/layout.tsx' app/not-found.tsx
• pnpm exec prettier --check 'app/(dashboard)/layout.tsx' app/not-found.tsx styles/dashboard.module.css styles/shared.module.css
• pnpm run type-check
• pnpm run build

[chatgpt-codex-connector]

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[chatgpt-codex-connector]

Avoid rendering duplicate headers on Layout pages

On routes covered by this dashboard layout that already render components/layouts/Layout (for example /content-adaptation, /automation, /campaigns, and /series), that component renders its own ScrollingHeader at components/layouts/Layout.tsx:51. Adding Header here means those authenticated pages now show two sticky navigation bars, duplicating the app chrome and reducing usable viewport; either only render this header for pages without the shared Layout wrapper or remove the nested page-level header layout there.

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